When I was 4 years old, (roughly 1970) we went to the library in Red Oak, IA for story books.  My mother remembers this book as well. It sparked my love for reading, and I would like to find it again, and read it to my grandchildren.  It was about the size of the Little Golden Books.  The story is of a little girl witch and her mother is a witch and they make blueberry muffins. The recipe was included in the back of the book. I was so thrilled to make the blueberry muffins and have remembered that book every time I’ve made muffins for so many years. I think it states in the story that if you use the blue berry juice, the muffins will be purple. 
The only one I’ve been able to find is the Old Black Witch – which is Not the same story.